Technical Field
The present disclosure relates generally to the field of drilling subterranean boreholes or wellbores, and more particularly to axial vibration of drillstring during drilling operations.
Background Art
Drilling of extended reach and/or deviated subterranean wells frequently suffer from sticking, sometimes referred to as differential sticking, and/or low rate of penetration. Weight on a drill bit decreases as the deviation angle increases, and frictional forces on lower outside surfaces of drillstrings increases as deviation angle increases. Drill cuttings and sediment collect on the bottom of borehole walls, especially in horizontal drilling, further increasing friction, in extreme cases to the point where a drillstring may not be movable with out some force being imposed on the drillstring. The best way to free a stuck drillstring and improve rate of penetration of the drill bit is to avoid sticking in the first place. It would be advantageous to be able to vibrate a drillstring efficiently, especially in the axial or longitudinal direction of the drillstring, and with as little change in present equipment and operations as possible.
U.S. Pat. No. 7,410,013 discloses boring and drilling apparatus including a rotatable drive shaft, and a cam member and followers for converting rotational motion into reciprocal motion, and a shroud having a cutting edge driven by the cam member and followers. The shroud may be selectively engageable with the cam member and followers, allowing the drive shaft to be removed through the shroud. Also described is a drill string incorporating a similar arrangement, allowing the drill string to be reciprocated within a bore. While an advance in the art, these mechanisms require stud-like cam followers positioned transversely to the drillstring in one or more cam tracks on a stationary member. The cam followers may thus be subject to severe shear forces, requiring frequent replacement, and the cam tracks may become clogged or damaged by the severe down hole conditions.
U.S. Pat. No. 4,408,670 discloses a sub assembly to be inserted between a drill string and a bit having a stabilizer sleeve to engage the walls of a bore hole and hold a first cam against rotation. A second cam is fixed to a drill holder at the lower end of the assembly and is driven in rotation by a rotary driving member extending through the assembly. The cams interengage so that relative rotation between them applies periodic impacts to the drill holder.
U.S. Pat. No. 6,508,317 discloses a downhole flow pulsing apparatus comprising a housing for location in a drillstring, the housing defining a throughbore to permit passage of fluid through the housing. A valve is located in the bore and defines a flow passage. The valve includes a valve member movable to vary the area of the passage to provide a varying fluid flow therethrough. A fluid actuated positive displacement motor is associated with the valve member. In a preferred embodiment, the apparatus is provided in combination with a drill bit and a pressure responsive device, such as a shock-sub, which expands or retracts in response to the varying drilling fluid pressure created by the varying flow passage area. The expansion or retraction of the shock-sub provides a percussive effect at the drill bit. In these types of tools, the fluid surface pumps must generate sufficient pressure to first run the rotor of the downhole positive displacement motor, then sufficient pressure to pass through the varying flow passage area, and lastly build fluid pressure in the shock-sub to provide the percussive effect at the drill bit.
It would be advantageous to be able to more efficiently axially vibrate a drillstring using a positive displacement power section, with as little change in present equipment and operations as possible.